1. Technical Field
The present disclosure relates, for example, to a variable nozzle unit that adjusts a passage area (throat area) for an exhaust gas to be supplied to a turbine wheel side in a variable geometry system turbocharger.
2. Description of the Related Art
In recent years, various types of development have been made on variable nozzle units used in variable geometry system turbochargers (see Japanese Patent Application Laid-Open Publication Nos. 2013-2293 and 2011-247189). Conventional variable nozzle units have the following specific configuration.
A first nozzle ring is disposed in a turbine housing in the variable geometry system turbocharger. The first nozzle ring has plural bottomless (penetrated) first supporting holes formed at intervals in a circumferential direction (in a predetermined circumferential direction). A second nozzle ring is integrally formed with the first nozzle ring. The second nozzle ring is provided at a location axially (in the axial direction of a turbine wheel) spaced apart from and opposite to the first nozzle ring. Furthermore, the second nozzle ring is located on a side further away from the bearing housing of the variable geometry system turbocharger (on a side opposite to the bearing housing) than the first nozzle ring. In addition, the second nozzle ring has plural bottomless (penetrated) second supporting holes formed so as to match the plural first supporting holes of the first nozzle ring.
The first nozzle ring and the second nozzle ring have facing surfaces facing each other. Plural variable nozzles are disposed at intervals in the circumferential direction (in a predetermined circumferential direction) between the facing surface of the first nozzle ring and the facing surface of the second nozzle ring. Each of the variable nozzles can rotate in an opening or closing direction (forward or reverse direction) around its shaft center, which is parallel to the shaft center of the turbine wheel. Each of the variable nozzles has a first nozzle shaft integrally formed on one side surface (one end surface). The first nozzle shaft is rotatably supported with a corresponding first supporting hole of the first nozzle ring. Furthermore, each of the variable nozzles has a second nozzle shaft integrally formed on the other side surface (the other end surface). The second nozzle shaft is rotatably supported with a corresponding second supporting hole of the second nozzle ring. In addition, a first nozzle flange (a first inner nozzle flange and a first outer nozzle flange) is integrally formed on a base end side of the first nozzle shaft on a blade surface (a blade surface inside in the radial direction and a blade surface outside in the radial direction) of each of the variable nozzles. Moreover, a second nozzle flange (a second inner nozzle flange and a second outer nozzle flange) is integrally formed on a base end side of the second nozzle shaft on a blade surface of each of the variable nozzles.
The first nozzle flange of each of the variable nozzles is configured to be able to contact the facing surface of the first nozzle ring. Therefore, it is possible to suppress the entry of foreign substances such as soot into the first supporting hole of the first nozzle ring by closing the gap between the inner peripheral surface of the first supporting hole of the first nozzle ring and the outer peripheral surface of the first nozzle shaft of the variable nozzle. Furthermore, the second nozzle flange of each of the variable nozzles is configured to be able to contact the facing surface of the second nozzle ring. Therefore, it is possible to suppress the entry of foreign substances into the second supporting hole of the second nozzle ring by closing the gap between the inner peripheral surface of the second supporting hole of the second nozzle ring and the outer peripheral surface of the second nozzle shaft of the variable nozzle. In addition, the first nozzle flange and the second nozzle flange of each of the variable nozzles are configured to be able to contact the facing surface of the first nozzle ring and the facing surface of the second nozzle ring, respectively. Therefore, it is possible to suppress tilting of the variable nozzle (the shaft center of the variable nozzle) by stabilizing the supporting state of the variable nozzle by the facing surface of the first nozzle ring and the facing surface of the second nozzle ring.
A link mechanism for synchronously rotating the plural variable nozzles is disposed on an opposite surface side of the facing surface of the first nozzle ring. As the link mechanism synchronously rotates the plural variable nozzles in the forward direction (opening direction), the passage area (throat area) for an exhaust gas to be supplied to the turbine wheel side increases. As the link mechanism synchronously rotates the plural variable nozzles in the reverse direction (closing direction), the passage area for the exhaust gas to be supplied to the turbine wheel side decreases.